The present invention relates to a slowing device within a receiving station of a machine for working elements in sheets.
Such a machine usually comprises an insertion station in which a stack of sheets is installed. The sheets are taken off successively from the top of this stack to be sent to a feed board. On this board, each sheet is placed in position before its traverse edge is gripped by a series of transporting pincers distributed along a transverse bar, also called a pincer bar. The ends of the pincer bar are secured to lateral drive chains. These transporting pincers drive the sheets through the various workstations of the machine. These workstations may in particular be a cutting station followed by a cutout ejection station, in order to culminate in a receiving station in which each sheet is released by the transporting pincers onto the top of a stack formed on a clearance pallet.
To ensure that the sheet falls uniformly, the sheet should be as flat as possible when stopped, at the moment of opening of the transporting pincers. Accordingly, the sheet is first held on its arrival in the station by a rear table and optionally by two side tables, which retract thereafter to allow the sheet to fall.
Because of the weakening of the sheets following the cutting and cutout ejection operations, the sheets no longer form anything more than fragile gratings of waste and because of the high speed at which these gratings arrive at the receiving station, slowing only by deceleration of the transverse pincer bar risks causing the rear portion of the grating to buckle and the rear portion tends to catch up with the front portion. This grating of waste must therefore be slowed by a matching device acting against its surface.
In patent CH 689 977 a device of this type has already been proposed comprising at least one flexible slowing member, consisting of a long brush extending transversely to the trajectory of the sheets and mounted so as to pivot about a transverse shaft, so that its trajectory about the shaft intersects the trajectory of the sheets. The direction of rotation of the end of the flexible slowing member intersects the trajectory of the sheets since it is opposed to the direction of movement of the latter. This device has driving means to cause the slowing means to pivot depending on the longitudinal dimension of the sheets and on their frequency of passage.
In this device, the movement of the slowing member is controlled by a rotary cam connected by a kinematic chain to the drive mechanism of the machine. This rotary cam acts on this slowing member by means of a horizontal runner with vertical movement, and the downstream portion of the runner has an upward oblique surface. Since the slowing member is mounted on a longitudinally movable frame, its movement remains constant for the sheets having a long longitudinal dimension, and then it reduces progressively as the frame advances facing the oblique portion of the horizontal runner.
With such a device, the movement of the slowing brush is optimal for one determined sheet format, to the detriment of the other formats. It is the passage of the pincer bar for transporting the sheets that determines the possibility of lowering the slowing brush. The kinematic connection between the control of descent of this brush and the drive mechanism of the machine forms a limitation to the accelerations communicated to the slowing brush.
Then another device of this type has been proposed in document EP 1 153 869, making it possible to respond to the problems posed by the previous system. In this device, the movements of the slowing member are generated by an electromechanical actuator connected to slaving means. This device gives total satisfaction, but it comprises costly elements which make its cost excessive for entry-level machines.